1. Field of the Invention
The present invention relates generally to an endless belt type bench testing apparatus, and more specifically, to an endless belt supporting structure for a bench testing apparatus for use in, such as, testing vehicular tires and vehicular performance, with an improved structure which ensures a dynamic pressure to be effectively generated between an endless belt and its supporting base.
2. Description of the Background Art
In an endless belt type bench testing apparatus, a flexible endless belt extending between a pair of rotary drums is used as a simulated road on which a vehicle tire or tires are placed, to perform a simulated road test which is equivalent to a test performed on an actual road. For example, in case of a vehicular tire test, a tire is placed on the endless belt to measure deformation of the tire or tire tread at various tire loads with various slip angles or camber angles or the like applied to the tire, as well as to measure a torque exerted on the drum, or the like. On the other hand, in case of a vehicular bench test on a chassis dynamometer, a fuel economy test, an engine performance test, an endurance test or the like is performed by placing all of the tires of the vehicle on the endless belt.
The endless belt type bench testing apparatus utilizes a hydraulic supporting structure for supporting the endless belt aginst the tire load as well as for ensuring a smooth movement of the belt which is driven by the tire or tires. Two types of the hydraulic belt supporting structure are known in the art, one using a dynamic pressure of a liquid lubricating medium and the other using a static pressure of the liquid lubricating medium.
Japanese Patent First (unexamined) Publication (Tokkai) Showa No. 56-129836 discloses the endless belt type bench testing apparatus which utilizes the dynamic pressure of the supporting liquid medium. In the disclosed structure, a supporting base is provided between the pair of the drums and beneath the endless belt in a manner to define a small clearance gap between the endless belt and the supporting base. The liquid medium, such as, water is supplied into the clearance gap for generating the dynamic pressure in the form of a thin liquid layer between the endless belt and the supporting base so as to support the belt against the tire load.
Specifically, an upper surface of the supporting base facing the belt is formed with a plurality of water supply ports in the form of elongate grooves each extending in a direction perpendicular to a running direction of the endless belt substantially over a width of the endless belt. The water supply ports are arranged at a predetermined interval along the belt running direction and define land portions between the adjacent ports. Each port is provided at its bottom with a water supply hole communicating with a water supply source through a water supply path formed in the supporting base. When the vehicular tire mounted on the endless belt is driven with the pressurized water supplied into the water supply ports, the dynamic pressure in the form of a thin liquid layer is hydraulically generated in the clearance gap between the endless belt and the land portions of the supporting base upper surface, so as to support the endless belt against the tire load.
On the other hand, Japanese Patent First (unexamined) Publication (Tokkai) Showa No. 55-128140 discloses the endless belt type bench testing apparatus which utilizes the static pressure of the liquid lubricating medium. In the disclosed structure, a number of water supply ports each having a circular shape in plan view are provided on the upper surface of the supporting base in place of the elongate grooves as mentioned above. The static pressure is generated in the clearance gap between the endless belt and the supporting base upper surface by supplying the highly pressurized water into the circular ports. The static pressure raises and supports the endless belt against the tire load.
In the bench testing apparatus utilizing the dynamic pressure, there is advantage that a small amount of the water is enough to effectively support the belt against the tire load, while there is disadvantage that, since the dynamic pressure necessary for supporting the belt is established by a stress which is generated by a shearing action of the water after the belt reaches a certain high speed, there is no dynamic pressure or only an insufficient dynamic pressure generated between the belt and the supporting base upper surface until the belt reaches the certain high speed. Accordingly, the belt contacts the supporting base upper surface under pressure due to the applied tire load, resulting in damages or breakages of the belt and the supporting base.
Further, since each elongate port is continuous in the direction perpendicular to the belt running direction, if the running belt is slanted due to bias or offset of the tire load applied to the belt, the running belt rises at a side where the applied tire load is smaller than that at the other side of the belt, resulting in leakage of the water to cause a dynamic pressure drop so that the effective supporting of the belt is not attained.
Further, in the above-noted Japanese Patent First (unexamined) Publication (Tokkai) Showa No. 56-129836, since each elongate port has a planar bottom, the water supplied into each elongate port is not effectively introduced by the running belt into the clearance gap between the running belt and the land portions of the supporting base upper surface due to an upright wall of each elongate port existing at its side downstream of the running belt, resulting in insufficient dynamic pressure generated between the running belt and the land portions.
Still further, since there is inevitably provided a land portion at an upstream end portion of the supporting base upper surface, i.e. the land portion being not defined by the adjacent elongate ports, no dynamic pressure is generated between the running belt and this land portion, resulting in possibility of damages of the belt and the supporting base.
On the other hand, in the above-noted Japanese Patent First (unexamined) Publication (Tokkai) Showa No. 55-128140 which utilizes the static pressure of the water, the above mentioned problems are not pertinent. However, since the running belt is supported by the static pressure of the water generated within the clearance gap between the belt and the supporting base upper surface, it is necessary to supply a large amount of the highly pressurized water into the circular ports, leading to the necessity of providing a large water supply equipment. Further, since a large amount of the water is circulated through a water supply circuit, a large equipment is also required for controlling a temperature of the water. Still further, since the highly pressurized water is used, the water is likely to dispersed out of the clearance gap between the running belt and the supporting base upper surface. Accordingly, a highly reliable sealing structure is also required.
Further, in the bench testing apparatus utilizing the dynamic pressure of the water, there has been proposed a supporting base which is constituted by first and second sections. The first section is disposed facing the belt with the predetermined clearance gap therebetween and is made of material, such as Teflon, for ensuring a smooth contact with the running belt so as to prevent the damages of the belt when the belt contacts with the first section under pressure due to the tire load, particularly during the speed of the running belt below the certain high speed as mentioned above. The second section is fixed to an underside of the first section by a plurality of bolts. Each bolt is inserted into a first mounting hole formed vertically through the first section and further into a second mounting hole formed in the second section for firmly connecting the first and second sections. The first mounting hole has a stepped shape having an upper larger diameter section for receiving a head of the bolt and a lower smaller diameter section. The bolt is inserted such that the bolt head is within the larger diameter section with some virtical distance between a surface level of the land portion and an upper end of the bolt head.
In this mounting structure, however, since the land portions include the recessed portions (the larger diamter sections of the first mounting holes), the water flows generated by the running belt are disturbed due to the existence of the recessed portions, resulting in generation of the insufficient dynamic pressure of the water.